The present invention relates, in general, to a feeding device for an automatic sewing arrangement for producing a stitch contour in a workpiece according to a predetermined program. A movably arranged workpiece receiving device is controlled with respect to the needle by means of a link system cooperating with a control cam. The link system is installed with two levers tiltably received on an axis of the stand of the sewing arrangement. In particular, new driving devices are proposed for operating the levers of the link system.
In the German laid-open patent application DE-OS 30 00 831, there is described such a sewing arrangement, which is installed essentially with a link system. The two drive levers of the link system are each formed with a cam-following means, each operating with a cam groove provided in the upper and lower side of a rotatably driven control cam. As the control cam rotates for one revolution, the workpiece clamp situated at a drive-off lever of the link system travels in the sewing plane as in a two-dimensional path according to the predetermined program. In the lower side of the control cam there is profiled a further control groove cooperating with an additional lever capable of rotating the workpiece clamp, turnably connected to the drive-off lever, where the lever is operably connected to the workpiece clamp by means of a timing belt drive.
Feeding devices of such construction are well proven in the field due to their simple construction and reliable operation. As all three control grooves are firmly positioned relatively to each other and commonly driven, a desired rotation of the workpiece clamp only also requires some lost space of the other two control grooves controlling the two-dimensional path of the workpiece clamp. Furthermore, the workpiece clamp is limited as to its movements of rotation, as it can only be rotated over a certain angle, that may have a value of 360.degree. at the most. Moreover, the two control grooves situated on one side of the control cam limit themselves in their extension so as to prevent any cross section, i.e. the work area of the workpiece clamp is restricted. In order to achieve the maximum of rotation of 360.degree., a large gear ratio for rotatably driving the workpiece clamp is required. This makes the drive system sensitive with respect to tolerances of the cam groove's geometry and also exposes the cam follower and the cam groove to increased wear. As the control cam cannot be enlarged without any limit actions, it is possible only to control a program provided with a limited number of stitches. Another shortcoming is represented by the fact that a control cam (once it is manufactured) cannot be altered anymore, so that a correction of a sewing program can be achieved only by replacing the control cam with another one.
In German Patent No. DE-PS 28 18 179 equivalent to U.S. Pat. No. 4,157,686, there is described a feeding device of the aforementioned kind, where the workpiece clamp is firmly connected to the drive-off lever and the control cam may be rotatably driven with different velocities so as to get a maximum sector of the control cam for use of the actual sewing program. This is achieved by the installation of additional drive and control elements.
It is a main object of the present invention to provide the known feeding device with drive elements so as to achieve universal movements of the workpiece clamp which are limited only by the size of the link system.
It is a further object of this invention to provide individual drive elements for each drive lever as to be completely free in controlling the movements of the workpiece clamp.
Another object of the present invention is to create a feeding device having a rotatable workpiece clamp with no limitation as far as the rotation of the workpiece clamp is concerned.
A further object is to minimize the mass of the rotatably driven workpiece clamp.
Another object is to provide an arrangement of the workpiece clamp drive, the movements of which do not interfere with the tilt movements of the levers induced by the drive devices.
Still another object of the present invention is to provide a feeding device with simple controllable drive motors controlled by a central programmable computer.
Still another object of the present invention is to provide a feeding device of the aforesaid character which is simple in construction and reliable in operation.